Sodium benzoate is recommended in food applications at an inclusion level of no more than 0.1%.
When preserving cosmetic and toiletry products it is generally accepted to be used at under 3% inclusion level.
It's effectiveness increases with lower pH levels, so inclusion levels may vary from one product to another.
Sodium Benzoate is not recomended for use in environments where the pH exceeds 4.5. If an aqueous solution has a pH level higher than 4.5 it is recommended to be pH-balanced with the addition of a suitable amount of an acid such as citric acid.